JPWO2011033948A1 - GLASS SUBSTRATE FOR INFORMATION RECORDING MEDIUM, INFORMATION RECORDING MEDIUM, AND METHOD FOR PRODUCING GLASS SUBSTRATE FOR INFORMATION RECORDING MEDIUM - Google Patents

Abstract

The objective is to provide a glass substrate for information recording media capable of obtaining a low GA value. The arithmetic average waviness Wa of the surface is less than 0.6 nm, the radial direction, and the measurement wavelength is 80 μm or more and 120 μm or less. The root mean square height Rq of the microwaviness in the range is less than 0.01 nm.

Description

  The present invention relates to a glass substrate for information recording medium, an information recording medium, and a method for manufacturing a glass substrate for information recording medium.

  An aluminum substrate has been widely used as a substrate for a magnetic recording medium such as a magnetic disk as an information recording medium. However, as a magnetic disk becomes smaller and has a higher recording density, the strength and flatness of the recording surface are improved as compared with an aluminum substrate. It is being replaced by an excellent glass substrate.

  In recent years, there has been a demand for a reduction in magnetic head flying height (glide height) in order to improve recording density. To meet this requirement, the surface of the magnetic recording medium, that is, the surface of the glass substrate for the magnetic recording medium is extremely uniform. It is necessary to finish as a rough surface.

  Patent Document 1 discloses a magnetic disk in which minute waviness has a period of 0.1 mm to 5 mm and an amplitude of 0.1 nm to 1 nm.

  In Patent Document 2, the amplitude Wa of the undulation on the surface when measured at a measurement wavelength of 5.0 mm is in the range of 0.1 nm to 0.5 nm, and the above undulation when measured at a measurement wavelength of 30 μm to 200 μm. A magnetic disk substrate is disclosed in which the average amplitude Wb of the micro waviness formed in the above is 0.3 nm or less, and the value Wb / Wa obtained by dividing the average amplitude Wb of the micro waviness by the amplitude Wa of the waviness is 0.6 or more. ing.

  The evaluation of the flying height of the magnetic head may be indicated by a glide avalanche value (GA value) (for example, Patent Document 3). The magnetic recording medium becomes suitable for high recording density when the GA value becomes smaller.

JP 2000-207733 A JP 2007-164916 A JP 2003-173517 A

  However, a desired low GA value cannot be obtained even when the conditions that define the shape of the magnetic disk or the magnetic disk substrate described in Patent Document 1 and Patent Document 2 are satisfied.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to provide a glass substrate for an information recording medium capable of obtaining a low GA value, and information recording using the glass substrate for the information recording medium. It is to provide a method for producing a medium and a glass substrate for an information recording medium.

  Said subject is solved by the following structures.

1. The surface arithmetic mean waviness Wa is less than 0.6 nm,
A glass substrate for an information recording medium, characterized in that a root mean square height Rq of micro-waviness in a radial direction and a measurement wavelength in the range of 80 μm to 120 μm is less than 0.01 nm.

  2. 2. The glass substrate for an information recording medium according to 1, wherein the arithmetic average waviness Wa is less than 0.55 nm and the root mean square height Rq of the microwaviness is less than 0.007 nm.

  3. 3. An information recording medium comprising a magnetic film on a surface of the glass substrate for information recording medium according to 1 or 2 above.

4). The polishing machine has a polishing step in which the weight of the surface plate is 600 kg / m ² or less and the rotational speed is 10 rpm or less,
The arithmetic average waviness Wa of the surface after the polishing step is less than 0.6 nm,
A method for producing a glass substrate for an information recording medium, characterized in that the root mean square height Rq of the microwaviness in the radial direction in the range of the measurement wavelength of 80 μm or more and 120 μm or less is less than 0.01 nm.

  5). 5. The glass substrate for an information recording medium according to 4, wherein the arithmetic average waviness Wa is less than 0.55 nm and the root mean square height Rq of the microwaviness is less than 0.007 nm. Method.

  According to the present invention, a glass substrate for an information recording medium capable of obtaining a low GA value, an information recording medium using the glass substrate for the information recording medium, and a method for manufacturing the glass substrate for an information recording medium are provided. Can do.

It is a figure which shows the whole glass substrate for information recording media. It is a figure which shows the example of the magnetic recording medium provided with the magnetic film on the front main surface of the glass substrate for information recording media. It is an enlarged view of the cross section of a glass substrate, (a) is a figure which shows the wave | undulation and micro wave | undulation of the glass substrate surface, (b) is a figure which expands a part of wave | undulation and shows the micro wave | undulation of substantially one period. is there. It is a figure which shows typically the surface shape of a magnetic disc, and the locus | trajectory which a head moves, (a) shows the case where the measurement wavelength L1 of micro waviness exceeds 120 micrometers, (b) shows the measurement wavelength L2 of micro waviness is less than 80 micrometers. This case is shown. It is a manufacturing process figure explaining the manufacturing process of the glass substrate for information recording media.

  Although the present invention will be described based on an embodiment, the present invention is not limited to the embodiment.

  FIG. 1 shows the overall structure of an information recording medium glass substrate 1 (hereinafter also referred to as a glass substrate 1) which is a substrate of a magnetic disk which is an information recording medium according to the present invention. As shown in FIG. 1, the glass substrate 1 has a donut-shaped disk shape with a hole 5 formed in the center. 10t is an outer peripheral end surface, 20t is an inner peripheral end surface, 7a is a front main surface, and 7b is a back main surface. FIG. 2 is a diagram showing an example of a magnetic recording medium (also referred to as a magnetic disk D) having the magnetic film 2 on the front main surface 7a of the glass substrate 1 shown in FIG. The magnetic film 2 can also be provided on the back main surface 7b.

  Enlarged views of the cross section of the glass substrate are shown in FIGS. A solid line in FIG. 3A is a measurement cross-sectional curve 11 indicating the surface shape of the glass substrate. Moreover, a broken line is the waviness curve 12 showing the waviness of the surface of a glass substrate. FIG. 3B is an enlarged view of a part of FIG. 3A, showing a fine waviness curve 13 that is a roughness curve generated on the waviness curve 12, and L represents a measurement wavelength. Show.

  In an HDD (Hard Disk Drive), information is read and written by magnetism when a head moves over a magnetic disk. In order for the magnetic disk to be able to cope with a high recording density, it is necessary that the head can perform recording and reproduction with a low flying height. In a magnetic disk inspection, as a method for evaluating the flying height of the head, there is a measurement of a glide avalanche value (GA value).

  The GA value of the present embodiment is the flying height when the flying height of the head is gradually lowered and the flying height of the head becomes unstable in the magnetic disk for inspection. The smaller the GA value, the smaller the flying height of the head with respect to the magnetic disk, and it is possible to cope with a high recording density.

  Until now, it was thought that the GA value was affected by the micro-waviness of the entire magnetic disk. However, the inventors have intensively studied how the GA value can be reduced. We found that radial waviness greatly affects the GA value. The inventors presumed that micro waviness seen from the radial direction closer to the movement of the head might have an effect on the GA value, and focused on the micro waviness in the radial direction of the magnetic disk, thereby reaching the present invention.

  Furthermore, it was found that when the measurement wavelength L of the microwaviness is limited to the range of 80 μm or more and 120 μm or less, the relationship between the GA value and the microwaviness is remarkable. Specifically, a value Rq (hereinafter referred to as root mean square height Rq) obtained by calculating a root mean square root height in the radial direction in the measurement wavelength L range of 80 μm to 120 μm is preferably less than 0.01 nm. It was found that a GA value sufficiently low in practical use can be obtained by setting the thickness to less than 0.007 nm.

  It is considered that the head can follow a micro swell exceeding the measurement wavelength L of 120 μm, and the micro swell of less than 80 μm is not an individual micro swell, but the head follows a virtual surface where these are conditioned. 4A and 4B, 8 schematically shows the surface shape of the magnetic disk, and H schematically shows the trajectory of the head. The measurement wavelength L1 of the fine undulation in FIG. 4A is a value exceeding 120 μm, and the measurement wavelength L2 of the fine undulation in FIG. 4B is a value less than 80 μm.

  The range where the measurement wavelength L of the microwaviness is 80 μm or more and 120 μm or less is considered to be a range close to the lower limit value at which the head can follow each microwaviness.

  If the measurement wavelength range is widened, Rq is expressed by the root mean square, which means that it will be averaged, and if the measurement range covers the waviness of the entire disk surface, Rq will be averaged, thus realizing a low GA. It is considered that the difference between the substrate that can be made and the substrate that is not so does not appear remarkably.

  In the above description, the microwaviness has been described. However, the small waviness on which the microwaviness is superimposed is also necessary for obtaining a low GA value, and the arithmetic average waviness Wa is less than 0.6 nm, preferably 0.8. It must be less than 55 nm.

  The undulation of the undulation curve 12 in FIG. 3A is measured over the entire surface of the glass substrate using a multi-function disk interferometer (Optiflat: manufactured by Phase Shift Technology. Inc.). The measurement principle is a method of measuring a subtle shape change of the surface by irradiating the surface of the glass substrate with white light and measuring an intensity change of interference between the reference light and the measurement light having different phases. The obtained measurement data is measured at a measurement wavelength of 0.1 mm to 5 mm, and the swell is measured, and the arithmetic average swell Wa is obtained according to JIS B0601: 2001.

  The micro waviness of the micro waviness curve 13 generated on the radial waviness curve 12 in FIG. 3B is measured by an optical surface analyzer OSA (CANDELA, RMS application). The measurement wavelength L is performed in a band of 80 μm or more and 120 μm or less, and the root mean square height Rq is obtained according to JIS B0601: 2001.

The measurement of the radial direction of the microwaviness using the optical surface analyzer OSA is performed by dividing the glass substrate into 125 parts at an angle of 2.88 ° in the circumferential direction and 0.89 μm steps in the radial direction from each of the divided inner diameters to outer diameters. Every time, the root mean square height Rq is calculated. The glass substrate according to the present invention has a root-mean-square height Rq of less than 0.01 nm in all 125 radial directions.
(Manufacturing process of glass substrate for information recording medium)
The manufacturing process of the glass substrate for information recording media will be described with reference to the manufacturing process diagram of FIG.

  There is no limitation on the size of the glass substrate. For example, there are glass substrates of various sizes such as an outer diameter of 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches. Further, the thickness of the glass substrate is not limited, and there are glass substrates having various thicknesses such as 2 mm, 1 mm, and 0.64 mm.

  First, a glass material is melted (glass melting step), molten glass is poured into a lower mold, and press molding is performed with an upper mold to obtain a disk-shaped glass substrate precursor (press molding process). Note that the disk-shaped glass substrate precursor may be produced by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using press molding.

As a material of the glass substrate, for example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) Aluminosilicate glass; borosilicate glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg) , Ca, Sr, Ba) and the like can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

  The press-molded glass substrate precursor is drilled in the center with a core drill or the like having a diamond grindstone or the like in the cutter (coring process).

  Next, both surfaces of the glass substrate are polished to preliminarily adjust the overall shape of the glass substrate, that is, the parallelism, flatness and thickness of the glass substrate (first lapping step).

  Next, the inner and outer diameters are processed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with, for example, a grinding wheel such as a drum-shaped diamond (inner / outer diameter processing step).

  Next, on the inner peripheral end surface of the glass substrate, the corners of the chamfered portion are curved by brush polishing using a polishing liquid, and fine scratches and the like are removed (inner peripheral end surface processing step).

  Next, both surfaces of the glass substrate are polished again to finely adjust the parallelism, flatness and thickness of the glass substrate (second lapping step).

  Then, the outer peripheral end surface of the glass substrate is subjected to brush polishing using a polishing liquid so that the corner portion of the chamfered portion is curved, and fine scratches and the like are removed (outer peripheral end surface processing step).

  The order from the first lapping step after the coring processing to the outer peripheral end surface processing step is not limited to that shown in FIG. 5 and can be changed as appropriate according to the situation. For example, the lapping process may be performed first, and then the inner / outer diameter machining process, the inner circumference, and the outer circumference end face machining process may be performed. Further, after the first lapping step and the inner / outer diameter machining step, a second lapping step, an inner circumference and an outer circumference end face machining step may be performed.

  A polishing machine that polishes the glass substrate in the first and second lapping steps will be described. As the polishing machine, a known polishing machine called a double-side polishing machine can be used. The double-side polishing machine includes a disk-shaped upper surface plate and a lower surface plate that are arranged vertically in parallel with each other, and rotate in opposite directions. A plurality of diamond pellets for polishing the main surface of the glass substrate are attached to the opposing surfaces of the upper and lower surface plates. The diamond pellet can be substituted by a resin sheet in which diamond abrasive grains are embedded. Between the upper and lower surface plates, there are a plurality of carriers that rotate in combination with an internal gear provided in an annular shape on the outer periphery of the lower surface plate and a sun gear provided around the rotation axis of the lower surface plate. The carrier is provided with a plurality of holes, and a glass substrate is fitted into the holes. The upper and lower surface plates, the internal gear, and the sun gear can be operated by separate driving.

  The polishing operation of the polishing machine is such that the upper and lower surface plates rotate in opposite directions, and the carrier sandwiched between the surface plates via the diamond pellets rotates with the surface plate holding a plurality of glass substrates. Revolves in the same direction as the lower surface plate with respect to the center of rotation. In such an operating polishing machine, the glass substrate can be polished by supplying a grinding liquid between the upper surface plate and the glass substrate, and the lower surface plate and the glass substrate.

When using this double-side polishing machine, the weight of the surface plate applied to the glass substrate and the number of rotations of the surface plate are adjusted as appropriate according to the desired polishing state. The weight in the first and second lapping steps is preferably 600 kg / m ² to 1200 kg / m ² . Further, the rotation speed of the surface plate is preferably about 10 to 30 rpm, and the rotation speed of the upper surface plate is preferably about 30% to 40% slower than the rotation speed of the lower surface plate. Increasing the load on the surface plate and increasing the rotation speed of the surface plate increases the amount of polishing, but if the load is increased too much, the surface roughness will not be good, and if the rotation speed is too high, the flatness will be good. Not. Further, when the load is small and the rotation speed of the surface plate is slow, the polishing amount is small and the production efficiency is lowered.

  Upon completion of the second lapping step, defects such as large waviness, chipping and cracks are removed, and the surface roughness of the main surface of the glass substrate is Rz (maximum height) of 2 μm to 4 μm, Ra (arithmetic mean roughness) Is preferably about 0.1 μm to 0.4 μm. By maintaining such a surface state, polishing can be efficiently performed in the first polishing step.

  In the first lapping step, roughly large undulations, chips and cracks are efficiently removed so that the second lapping step can be performed efficiently. For this reason, it is preferable to use diamond pellets of about # 800 mesh to # 1200 mesh coarser than # 1300 mesh to # 2200 mesh used in the second wrapping. The surface roughness at the time when the first lapping step is completed is preferably such that Rz is 4 μm to 8 μm and Ra is about 0.3 μm to 0.8 μm.

  The inner peripheral and outer peripheral end faces of the glass substrate are polished by brush polishing in the inner peripheral and outer peripheral end face processing steps. The brush is preferably made of nylon, polypropylene or the like having a diameter of about 0.2 to 0.3 mm. The polishing liquid is preferably cerium oxide having a particle size of about several μm. As a result of brush polishing, the surface roughness of the inner and outer end faces is preferably such that Rz is 0.2 μm to 0.4 μm and Ra is about 0.02 μm to 0.04 μm. The shape of the end surface of the glass substrate that has undergone the inner and outer diameter processing steps and the inner and outer peripheral end surface processing steps is such that the corner formed by the main surface and end surface is removed, and the position is about 0.2 mm to 0.5 mm from the outer peripheral end surface From the main surface.

  Here, Ra (arithmetic mean roughness) and Rz (maximum height) are defined in JIS B0601: 2001. These can be measured by an atomic force microscope (AFM) or the like. These rules and measurement methods also apply to Ra and Rz described below.

  In the above example, the diamond pellet and the grinding liquid are used when polishing the glass substrate. However, it is also possible to apply a polishing method by attaching a pad to the polishing surface of the upper and lower surface plates and supplying the polishing liquid. . Examples of the abrasive include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, colloidal silica, and diamond. These are dispersed in water and used as a slurry. The pad is divided into a hard pad and a soft pad, but can be appropriately selected and used as necessary. Examples of the hard pad include pads made of hard velor, urethane foam, pitch-containing suede, etc., and examples of the soft pad include pads made of suede, velor, etc.

  A polishing method using a pad and a polishing agent can cope with rough polishing to precision polishing by changing the particle size of the polishing agent and the type of the pad. Therefore, in the first lapping step and the second lapping step, the abrasive, the particle size of the abrasive, and the pad are appropriately combined so that the above-mentioned surface roughness can be obtained by efficiently removing large undulations, chips, cracks, etc. Can respond.

  Moreover, it is preferable to perform the washing | cleaning process for removing the abrasive | polishing agent and glass powder which remained on the surface of the glass substrate after the 1st and 2nd lapping process.

  It should be noted that the polishing machines used in the first lapping process and the second lapping process have the same configuration, but it is preferable to perform polishing using different polishing machines prepared exclusively for the respective processes. This is because the dedicated diamond pellets are pasted, so that the replacement is a large-scale operation, and complicated operations such as resetting the polishing conditions are required, resulting in a reduction in manufacturing efficiency.

  Following the outer peripheral end face polishing step, an annealing step is performed. In the annealing step, the glass substrate is placed in an electric heating furnace and held at a temperature of 200 ° C. or higher and 400 ° C. or lower for 10 to 120 minutes. The rate of temperature increase and the rate of temperature decrease are not particularly specified, but it is preferable to increase the temperature to a predetermined temperature in about 10 to 30 minutes and to cool down over a period of about 10 to 60 minutes. By this annealing process, the stress strain generated in the glass substrate in the conventional processing process can be released. In addition to air, the annealing step is preferably performed in an oil such as silicone oil that hardly deteriorates at an annealing temperature, in an inert gas such as argon gas or helium gas, or in nitrogen gas. When annealing is performed in such an atmosphere, ionized substances do not enter the glass substrate surface, so that the flatness of the glass substrate surface can be maintained.

  The next polishing step may be one step, but two steps are preferable, and two steps are used in the present embodiment. By performing the polishing process after the annealing process, stress strain is released inside the glass, cracks are not generated during the polishing process, and the incidence of defective products is reduced.

  First, in the first polishing step, the surface roughness is improved and the glass according to the present invention is improved in the second polishing step so that the surface roughness finally required in the second polishing step can be efficiently obtained. Polishing is performed so that the surface shape of the substrate can be obtained efficiently.

  The polishing method uses a polishing machine having the same configuration as the polishing machine used in the first and second lapping processes except that a suede pad and a polishing liquid are used instead of the diamond pellets and the grinding liquid used in the lapping process. .

  The pad is preferably a hard pad having a hardness A of about 70 to 90, for example, urethane foam. When the pad hardness becomes soft due to heat generated by polishing, the shape change of the polished surface increases, so it is preferable to use a hard pad. The abrasive is preferably used in the form of a slurry by dispersing cerium oxide or the like having a particle size of 0.2 to 1.5 μm in water. The mixing ratio of water and abrasive is preferably about 1: 9 to 3: 7.

Weighted on the glass substrate by platen, it can be adjusted arbitrarily, preferably the 1100 kg / ^{m 2} from 900 kg / ^{m 2} in terms of productivity. The load applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge. When the weight is increased, the inner side of the outer peripheral end portion tends to fall and rise toward the outside. Further, as the weight is decreased, the outer peripheral end portion tends to be close to a flat surface and the surface sagging increases. The weight can be determined while observing these trends.

  Moreover, in order to improve surface roughness, the rotation speed of the surface plate can be arbitrarily adjusted. From the viewpoint of productivity, the rotation speed of the upper surface plate is set to 30 rpm from the rotation speed of the lower surface plate. % To 40% is preferred.

  The polishing amount is preferably 30 μm to 40 μm depending on the above polishing conditions. If it is less than 30 μm, scratches and defects cannot be removed sufficiently. On the other hand, when the thickness exceeds 40 μm, the polishing is performed more than necessary, and the production efficiency is lowered.

  The second polishing step is a step of further precisely polishing the surface of the glass substrate after the first polishing step. The pad used in the second polishing step is a soft pad having a hardness of about 65 to 80 (Asker-C) softer than the pad used in the first polishing step, and it is preferable to use, for example, urethane foam or suede. As the abrasive, the same cerium oxide or colloidal silica as in the first polishing step can be used, but in order to make the surface of the glass substrate smoother, it is preferable to use an abrasive having a finer particle size and less variation. preferable. An abrasive having an average particle diameter of 10 nm to 50 nm, preferably about 20 nm, is dispersed in water to form a slurry, which is used as a polishing liquid.

  In the polishing liquid, the mixing ratio of water and abrasive is preferably about 1: 9 to 3: 7, and further, sulfuric acid or hydrogen peroxide is added to make the pH lower than 7, more preferably pH 2 or lower. And By making the polishing liquid acidic, agglomeration of the abrasive can be suppressed, polishing with the original particle size of the abrasive can be performed, and more precise polishing can be performed.

  In the polishing process, the glass substrate is loaded and processed as in the lapping process. By applying weight to the glass substrate, the waviness of the substrate is forcibly relaxed and polished in a flattened state. The polishing process causes the glass substrate to have less undulation, but if the weight is removed from the glass substrate, the undulation that was forcibly suppressed is restored, and the undulation is greater than before the weight removal.

In the second polishing step, the weight is 600 kg / m ² or less, which is less than the conventional weight, and the lower limit is not particularly defined, but the range of 550 kg / m ² to 600 kg / m ² is preferable from the viewpoint of productivity. When the weight is gradually reduced below 550 kg / m ² , the weight becomes insufficient for polishing the glass substrate, and more time is required for polishing, and finally it becomes impractical. End up.

By setting the load to 600 kg / m ² or less in the second polishing step, forced relaxation of the swell due to the load is reduced, and polishing is performed in a state closer to the swell of the glass substrate at this point. For this reason, after the polishing process, the return amount of the waviness after the weight removal is reduced, and the waviness and minute waviness of the glass substrate can be reduced.

  Moreover, the rotation speed of a surface plate shall be 10 rpm or less. When the rotational speed exceeds 10 rpm, vibration occurs in the rotating surface plate, and as a result, undulation occurs in the glass substrate. By setting the number of rotations of the surface plate to 10 rpm or less, vibration generated on the surface plate can be suppressed, and undulation and minute undulation generated on the glass substrate can be reduced. Although the lower limit is not particularly defined, if the rotational speed is gradually reduced, more time is required to perform polishing, and eventually it becomes impractical.

  By setting the weight on the glass substrate and the rotational speed of the surface plate as described above, the arithmetic mean waviness Wa is less than 0.6 nm, and the square mean of the microwaviness in the radial measurement wavelength L is in the range of 80 μm to 120 μm. The square root height Rq can be less than 0.01 nm.

  The polishing amount is preferably 2 to 5 μm. When the polishing amount is within this range, minute defects such as minute roughness and undulation generated on the surface and minute scratches generated in the process so far can be efficiently removed. When the polishing process is a single process, the first polishing process of the present embodiment may be omitted.

After completion of the second polishing step, the glass substrate is cleaned and inspected to complete the information recording medium glass substrate.
(Magnetic film formation)
FIG. 2 shows a perspective view of a magnetic disk D that is a magnetic recording medium in which a magnetic film is provided on the glass substrate described so far. In the magnetic disk D, a magnetic film 2 is directly formed on the surface of a circular glass substrate 1 for an information recording medium. As a method for forming the magnetic film 2, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on a substrate, or a method by sputtering or electroless plating is used. A method is mentioned. The film thickness by spin coating is about 0.3 μm to 1.2 μm, the film thickness by sputtering is about 0.04 μm to 0.08 μm, and the film thickness by electroless plating is 0.05 μm to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering and electroless plating is preferable.

The magnetic material used for the magnetic film is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Ni having a high crystal anisotropy is basically used, and Ni or A Co-based alloy to which Cr is added is suitable. Specific examples include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, and CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtSiO. The magnetic film may have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa) that is divided by a non-magnetic film (for example, Cr, CrMo, CrV, etc.) to reduce noise. In addition to the above magnetic materials, granular materials such as ferrite, iron-rare earth, and non-magnetic films made of SiO ₂ , BN, etc. in which magnetic particles such as Fe, Co, FeCo, CoNiPt are dispersed, etc. Also good. Further, the magnetic film may be either an inner surface type or a vertical type recording format.

  In addition, a lubricant may be thinly coated on the surface of the magnetic film in order to improve the sliding of the magnetic head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer that prevents wear and corrosion of the magnetic film include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers. Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxysilane is diluted with an alcohol-based solvent on the Cr layer, colloidal silica fine particles are dispersed and applied, and then baked to form a silicon dioxide (SiO ₂ ) layer. It may be formed.

  The glass substrate for an information recording medium according to the present invention is not limited to a magnetic recording medium (magnetic disk), and can be used for a magneto-optical disk, an optical disk, and the like.

The glass substrates and magnetic disks of Examples 1 to 4 and Comparative Examples 1 to 4 were produced as follows.
(Production of glass substrate)
Aluminosilicate glass (Tg: 500 ° C.) was used as a glass material, and a molten glass was press-molded to produce a blank material. A glass substrate having an outer diameter of 65 mm and an inner diameter of 20 mm was obtained through an inner and outer peripheral processing step and a lapping step. The thickness of the glass substrate was 0.64 mm.
(Annealing process)
As an annealing process, an electric heating furnace was used in an air atmosphere, and 100 glass substrates were respectively produced at an annealing temperature of 350 ° C. and an annealing time of 10 minutes. The temperature rising time from room temperature was 30 minutes, and the temperature lowering time to room temperature was 1 hour.
(Polishing process)
As the first polishing process, a urethane pad manufactured by Nitta Haas was used, and cerium oxide was used as the abrasive.

  As the second polishing step, a suede pad manufactured by FILWEL was used, and cerium oxide and colloidal silica were used as the abrasive.

As polishing conditions for the second polishing step, the hardness of the pad is 80 (Asker-C), the particle size of the abrasive is about 20 nm to 30 nm, and the polishing liquid is added with hydrogen peroxide to about pH 2, and the rotation speed of the upper and lower platen (rpm) The weighting (kg / m ² ) conditions are shown in Table 1.
(Washing process)
As a cleaning process, brush scrubbing with a roll scrubbing machine and cup scrubbing machine was performed, followed by cleaning with an ultrasonic cleaner.
(Measures swell height and micro swell)
Using Opti Flat (manufactured by Phase Shift Technology, measurement wavelength: 0.1 to 5 mm), the swell of the prepared glass substrate surface was measured, and the arithmetic average swell Wa was determined.

The height of the microwaviness in the measurement wavelength L range of 80 μm or more and 120 μm or less was measured using an optical surface analyzer OSA (CANDELA, RMS application), and the root mean square height Rq was obtained. The results are shown in Table 1.
(Production of magnetic disk)
On the surface of the obtained glass substrate, magnetic particles CoPt were sputtered to form a 0.05 μm magnetic film, thereby producing a magnetic disk.
(GA value measurement)
A magnetic disk is attached as an inspection disk to a dedicated device for GA value measurement, rotated at a constant speed, and the head is floated on the disk. In this state, while observing the signal from the head, depressurize the space where the head is floating on the inspection disk, and obtain the air pressure at which the signal from the head becomes unstable. The GA value was determined.

The GA value needs to be practically less than 3 nm, and as a determination in Table 1, it is indicated by symbols (◎, ○, ×) according to the following criteria.
A: Less than 2 nm B: 2 nm or more and less than 3 nm X: 3 nm or more

  As shown in Table 1, the magnetic average waving Wa is less than 0.6 nm and the root mean square height Rq of the microscopic waviness in the radial direction is less than 0.01 nm. Results were obtained.

1 Glass substrate for information recording media (glass substrate)
2 magnetic film 5 hole 7a front main surface 7b back main surface 10t outer peripheral end surface 11 measurement cross-section curve 12 waviness curve 13 micro waviness curve 20t inner peripheral end surface D magnetic disk

Claims (5)

The surface arithmetic mean waviness Wa is less than 0.6 nm,
A glass substrate for an information recording medium, characterized in that a root mean square height Rq of micro-waviness in a radial direction and a measurement wavelength in the range of 80 μm to 120 μm is less than 0.01 nm.   2. The glass substrate for an information recording medium according to claim 1, wherein the arithmetic average waviness Wa is less than 0.55 nm, and the root mean square height Rq of the minute waviness is less than 0.007 nm.   An information recording medium comprising a magnetic film on a surface of the glass substrate for information recording medium according to claim 1 or 2. The polishing machine has a polishing step in which the weight of the surface plate is 600 kg / m ² or less and the rotational speed is 10 rpm or less,
The arithmetic average waviness Wa of the surface after the polishing step is less than 0.6 nm,
A method for producing a glass substrate for an information recording medium, characterized in that the root mean square height Rq of the microwaviness in the radial direction in the range of the measurement wavelength of 80 μm or more and 120 μm or less is less than 0.01 nm.   5. The glass substrate for an information recording medium according to claim 4, wherein the arithmetic average waviness Wa is less than 0.55 nm and the root mean square height Rq of the microwaviness is less than 0.007 nm. Production method.